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The Mole and Stoichiometry

5 dot points across 5 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

Why must a chemical equation be balanced, and how do coefficients express conservation of mass and charge?

Balancing equations and conservation of mass: balance chemical equations by adjusting coefficients so atoms and charge are conserved, and interpret the coefficients as mole ratios.
A focused Regents Chemistry answer on balancing chemical equations: why mass and charge are conserved, how to adjust coefficients (never subscripts), and how the balanced coefficients give the mole ratios used in all stoichiometry.
9 min answer →

How do you write a correct chemical formula, and how do you find the percent by mass of an element in a compound?

Chemical formulas and percent composition: write formulas for ionic and molecular compounds using oxidation numbers and Table E, and calculate percent composition by mass using Table T.
A focused Regents Chemistry answer on writing chemical formulas and calculating percent composition: balancing charges with oxidation numbers and the Table E polyatomic ions, and the Table T percent-composition formula with worked examples.
9 min answer →

How do the coefficients in a balanced equation let you calculate the mass or moles of one substance from another?

Stoichiometric calculations: use mole ratios from a balanced equation to convert between moles and masses of reactants and products.
A focused Regents Chemistry answer on stoichiometry: using the mole ratios from a balanced equation together with gram-formula mass to convert between moles and masses of reactants and products, with worked mole-mole and mass-mass examples.
9 min answer →

How does the mole connect the mass of a sample to the number of particles it contains?

The mole and molar mass: use the mole and gram-formula mass to convert between the mass of a substance, the number of moles, and the number of particles.
A focused Regents Chemistry answer on the mole and gram-formula mass: Avogadro's number, how to find the molar mass from the periodic table, and the mass-mole-particle conversions, using the mole formulas on Table T of the Reference Tables.
9 min answer →

How can chemical reactions be classified, and how do you predict the products of each type?

Types of chemical reactions: classify reactions as synthesis, decomposition, single replacement, double replacement or combustion, and use Table J and Table F to predict whether a reaction occurs.
A focused Regents Chemistry answer on classifying reactions as synthesis, decomposition, single replacement, double replacement or combustion, and using the Table J activity series and Table F solubility guidelines to predict products and precipitates.
9 min answer →